The migration of lithium cations into the lattice of dioctahedral clay
s upon heating, considered up to now as irreversible, has been investi
gated. The samples under examination are two lithium-saturated montmor
illonites, selected with different charge-deficit distributions betwee
n the tetrahedral and octahedral sheets, to obtain direct information
on the structural changes occurring in both layers. Reexpansion of the
se samples previously collapsed at 300 degrees C has been attained, fo
r the first time, under high vapor water pressures. A structural chara
cterization of the smectites under the different treatments has been m
onitored by means of X-ray diffraction, XRD, Fourier transform infrare
d spectroscopy, FTIR, and Si-29, Al-27, and Li-7 magic angle spinning
nuclear magnetic resonance, MAS-NMR. The effect that Li+ ions exert on
the quadrupolar coupling constant of tetrahedral Al ions has been sho
wn. Direct experimental evidence on the location of lithium ions in th
e hexagonal holes of the collapsed structure is provided. Additionally
, generation of protons during the rehydration process is concluded.